Photon conversion materials do not exhibit one hundred percent efficiency, and thus some photons in received bands are not successfully converted to photons in converted bands. Moreover, photon conversion materials emit photons in converted bands in every direction, and thus some converted photons are emitted in directions other than toward a sensor that is configured to detect the converted photons. It would be desirable to increase the efficiency of the conversion of photons in received bands into photons in converted bands, and to increase the quantity of converted photons that are directed toward and detected by a sensor.